Process for producing tissue paper

ABSTRACT

The invention relates to a process for producing a tissue web, which is produced from a stock suspension including fibers. In this case, the volume and the tearing length are to be improved with the lowest possible freeness by the stock suspension containing lignocellolosic fibrous material made of wood or annual plants which has a tearing length of more than 6.5 km at 12°SR or a tearing length of more than 8.0 km at 15°SR and a lignin content of at least 15%, based on the oven-dry fibrous material, for coniferous wood in the unbleached state, or a tearing length of more than 4.5 km at 20°SR and a lignin content of at least 12%, based on the oven-dry fibrous material, for deciduous wood in the unbleached state, or a tearing length of more than 3.5 km at 20°SR and a lignin content of at least 10%, based on the oven-dry fibrous material, for annual plants in the unbleached state.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation of PCT application No. PCT/EP2007/010165,entitled “METHOD FOR THE PRODUCTION OF TISSUE PAPER”, filed Nov. 23,2007, which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a process for producing a tissue web, which isproduced from a stock suspension including fibers.

The invention also relates to a process for producing a stock suspensionfor use in particular for the production of tissue webs.

2. Description of the Related Art

Tissue products are currently mainly produced from fully cellulosicmaterials, in particular kraft pulps.

Mechanically produced fibrous materials find only limited use, sincehere the tendency to yellowing and the poor strength properties of thestocks prevent widespread use.

Common mixture ratios between long fiber and short fiber stocks lie inthe region of 50:50.

The porosity and the permeability of the tissue paper are determinedcritically by the freeness of the fibers in the stock suspension fromwhich the tissue paper is produced.

Here, a high freeness necessitates a high content of fines in thesuspension, which leads to lower porosity and permeability.

Furthermore, a high freeness causes a high water retention value for thefibers of the stock suspension, which means that the tissue paper isdifficult to dewater during its production.

At high machine speeds, the poor dewatering ability often results in toolow a dryness during production.

For instance, before the Yankee drying cylinder a certain dryness isneeded in order to prevent lifting of the tissue paper web as a resultof its contact with the hot circumferential surface of the tissue dryingcylinder.

In addition, the tissue must be tear-resistant. The tearing strength isdetermined both by the production process and by the freeness of thefibers. In order to increase the tearing strength, the tissue paper mustbe consolidated during its production. In order to obtain a high tearingstrength, the proportion of fines must also be high.

The requirements on the tearing strength thus contradict therequirements on the water absorption capacity, the absorbency and thedewatering ability.

What is needed in the art is the production of tissue paper with a highspecific volume, as high a tearing length as possible, with the lowestpossible freeness.

SUMMARY OF THE INVENTION

The present invention provides that the stock suspension containslignocellulosic fibrous material made of wood or annual plants which hasa tearing length of more than 6.0 km at 12°SR (°SR being the SchopperRiegler value) or a tearing length of more than 7.5 km at 15°SR and alignin content of at least 15%, based on the oven-dry fibrous material,for coniferous wood in the unbleached state, or a tearing length of morethan 4.5 km at 20°SR and a lignin content of at least 12%, based on theoven-dry fibrous material, for deciduous wood in the unbleached state,or a tearing length of more than 3.5 km at 20°SR and a lignin content ofat least 10%, based on the oven-dry fibrous material, for annual plantsin the unbleached state.

The fibers already exhibit high strength values at a freeness which isfar lower as compared with fibers used hitherto. The fibrous materialaccording to the invention is already capable of forming good bonds withneighboring fibers at a lower freeness and therefore also with a lowerexpenditure of refining energy.

The lignin content of the unbleached fibrous material in the case ofconiferous wood can advantageously include at least 15%, preferably atleast 18%, in particular at least 21%, of the oven-dry fibrous material,in the case of deciduous wood at least 12%, preferably at least 14%, inparticular at least 16%, of the oven-dry fibrous material and, in thecase of annual plants, at least 10%, preferably at least 12% and inparticular at least 19%, of the oven-dry fibrous material.

The higher the lignin content of the fibrous material, the lower are thelosses of woody substance during production of the fibrous material.

In this case, it is entirely possible to achieve even higher strengthvalues. Therefore, the tearing length for coniferous wood fiber stock at12°SR should be greater than 7 km, preferably greater than 7.5 km and inparticular greater than 8 km. The tearing length for coniferous woodfiber stock at 15°SR should be greater than 9 km, preferably greaterthan 9.5 km and in particular greater than 10 km.

The tearing length for deciduous wood fiber stock at a lignin content ofat least 12% and a freeness of 20°SR should be greater than 6 km,preferably greater than 7 km and in particular greater than 7.5 km.

The tearing length for annual plant fiber stock at 20°SR should begreater than 3.5 km, preferably greater than 4 km and in particulargreater than 4.5 km.

However, the fibrous material according to the invention is not justdistinguished by high tearing lengths. Instead, the strength leveloverall is high.

If the fibrous material according to the invention is subjected to ableaching treatment, the fiber properties are enhanced considerably. Thebleaching treatment is required for many applications with higherrequirements on the whiteness. However, it is also aimed at the settingand improvement of the fiber properties. With the bleaching treatment,the tearing lengths increase.

Thus, the stock suspension should contain lignocellulosic fibrousmaterial made of wood or annual plants which has a tearing length ofmore than 7.5 km at 15°SR and a lignin content of at least 13%, based onthe oven-dry fibrous material, for coniferous wood in the bleachedstate, or a tearing length of more than 5.0 km at 20°SR and a lignincontent of at least 10%, based on the oven-dry fibrous material, fordeciduous wood in the bleached state, or a tearing length of more than5.5 km at 20°SR and a lignin content of at least 10%, based on theoven-dry fibrous material, for annual plants in the bleached state.

Here, too, higher tearing lengths are advantageous. Thus, the tearinglength for coniferous wood fiber stock at 15°SR should be greater than 9km, preferably greater than 10 km.

The tearing length for deciduous wood fiber stock at 20°SR should begreater than 5.5 km and the tearing length for annual plant fiber stockat 25°SR should be greater than 5 km, preferably greater than 5.5 km andin particular greater than 6 km.

In order to be able to make optimal use of the advantages with respectto a high specific volume and high strength at the lowest possiblefreeness, the stock suspension should exclusively containlignocellolosic fibrous material according to the above description.

For many applications, however, it is sufficient if the stock suspensionis only partly formed from such lignocellulosic fibrous material. Inthis case it is advantageous if between 20 and 80%, preferably between30 and 50%, of the fibrous material of the stock suspension is formedfrom lignocellulosic fibrous material according to the abovedescription.

Following the formation of a tissue web, this is preferably led betweenan upper structured and permeable belt and a lower permeable belt in adewatering step, pressure being exerted on the upper belt, the tissueweb and the lower belt along a dewatering section.

The pressure exerted on the arrangement including the upper belt, tissueweb and lower belt can be effected by a gas flow and/or by a mechanicalpressing force.

Preferably, during a dewatering step, a gas flows firstly through theupper belt, then the tissue web and then the lower belt. In this case,the dewatering takes place in the direction of the lower belt.

Additionally or alternatively to the through-flow of gas, it may beadvantageous if, during the dewatering step, the arrangement includingthe upper belt, tissue web and lower belt is led in at least somesections between a press belt under tension and a smooth surface, thepress belt acting on the upper belt and the lower belt being supportedon the smooth surface.

Preferably, the gas flow flows through the arrangement including theupper belt, tissue web and lower belt, at least in some sections in theregion of the dewatering section, so that the dewatering is carried outsimultaneously by the pressing force of the press belt and thethrough-flow of the gas.

Trials have shown that the gas flow through the tissue web should amountto about 150 m³ per minute and meter length along the dewateringsection.

In the interests of adequate dewatering of the tissue web, the pressbelt should be under a tension of at least 30 kN/m, preferably at least60 kN/m and in particular 80 kN/m.

In order to be able to achieve good dewatering of the tissue web by wayof the mechanical tension of the press belt and also on account of thegas flow through the press belt, the press belt should have an open areaof more than 50% and a contact area of at least 15%.

The smooth surface is preferably formed by the circumferential surfaceof a roll. The gas flow can advantageously be produced via a suctionzone in the roll and/or a positive pressure hood arranged above theupper belt.

During the production of the lignocellulosic fibrous material accordingto the invention, it is important that at least a proportion of thestock suspension is produced from wood or annual plants having a lignincontent of at least 15% for coniferous wood and 12% for deciduous woodand 10% for annual plants, in each case based on the oven-dry fibermass, by the following steps:

-   -   producing a chemical solution with more than 5% of chemicals        (calculated as NaOH) for coniferous wood or with more than 3.5%        of chemicals (calculated as NaOH) for deciduous wood or with        more than 2.5% of chemicals (calculated as NaOH), in each case        based on the oven-dry quantity of the wood used,    -   mixing the chemical solution with the wood or annual plants in a        prescribed liquor ratio,    -   heating the chemical solution and the wood or annual plants to a        temperature above room temperature and then either (1st        alternative)    -   removing free-flowing chemical solution and    -   digesting the wood or annual plants in the vapor phase or (2nd        alternative)    -   digesting the wood or annual plants in the presence of the        chemical solution in liquid phase and    -   separating the free-flowing chemical solution and the wood or        annual plants.

The process according to the invention is based on the fact that, inorder to produce high-yield fibrous materials, higher quantities ofchemicals are used than were previously usual. More than 5% of chemicalsfor coniferous wood is considerably above the quantities of chemicalspreviously usual for industrial fibrous material production, likewisemore than 3.5% of chemicals for deciduous wood and 2.5% for annualplants. This high use of chemicals produces fibrous materials with goodyield and excellent strength properties. Thus, for coniferous wood atfreenesses of only 12°SR to 15°SR, tearing lengths of more than 8 km butalso tearing lengths of more than 9 km and more than 10 km are measured.For deciduous woods at only 20°SR, values of more than 5 km but alsotearing lengths of more than 6 km and more than 7 km are measured. Thedesired high strength level is therefore achieved.

It is to be viewed as an extraordinary advantage of the processaccording to the invention that the strength values are already achievedat extremely low freenesses, such as were not available hitherto forhigh-yield fibrous materials. Fibrous materials according to the priorart do not exhibit an acceptable strength level at freenesses of 12°SRto 15°SR for coniferous wood fibrous materials or of 20°SR for deciduouswood. Known fibrous materials at these low freenesses have until nowresulted in fibers which have not demonstrated adequate strengthproperties for economic use of such fibers.

Suitable annual plants are in particular bamboo, hemp, rice straw,bagasse, wheat, miscanthus and the like.

On the other hand, at freenesses in the range from 12°SR to 15°SR, thefibrous materials produced by the process of the invention already havetearing lengths of more than 8 km up to 11 km and tear propagationresistances of more than 70 cN up to more than 110 cN, based on a sheetweight of 100 g/m2. These low freenesses are moreover achieved with alow specific requirement for refining energy, which is less than 500kWh/t of fibrous material for coniferous wood; in the case of deciduouswood the need for refining energy can even be less than 300 kWh/t offibrous material. The finding that the high strength level is alreadyreached at low freenesses of 12°SR to 15°SR for coniferous wood and at20°SR for deciduous wood and less is a substantial part of theinvention.

These high strength values in combination with low freenesses forfibrous materials with a lignin content of more than 15% for coniferouswood fibrous materials, of more than 12% for deciduous wood fibrousmaterials or of more than 10% for annual plants, have hitherto not beenknown. The high strength level can, however, also be maintained forfibrous materials having an even higher lignin content. The processaccording to the invention is even suitable for producing coniferouswood fibrous materials having a lignin content of more than 18%,preferably more than 21%, advantageously more than 24%, based on theoven-dry fiber mass. Deciduous wood fibrous materials having a lignincontent of more than 14%, preferably more than 16%, particularlypreferably more than 18%, and also annual plants having a lignin contentof more than 10%, preferably more than 12%, in particular more than 19%,can likewise be produced with the process according to the invention andexhibit a high strength level.

The composition of the chemical solution used for the digestion can bedefined in accordance with the wood or annual plants used for thedigestion and the desired fibrous material properties. As a rule, only asulfite component is used. Alternatively or as a supplement, a sulfidecomponent can also be added. Digestion with a sulfite component is notdisrupted by the presence of sulfide components. Industrially, sodiumsulfite is normally used but the use of ammonium or potassium sulfite orof magnesium bisulfite is also possible. In particular if highquantities of sulfite are used, it is possible to dispense with the useof an alkaline component since a high pH, which encourages digestion, isestablished even without the addition of alkaline components.

In order to adjust the pH and to assist the delignification, an acidand/or an alkaline component can also be metered in. Industrially, thealkaline component used is normally sodium hydroxide (NaOH). However,the use of carbonates is also possible, in particular sodium carbonate.All statements relating to quantities of chemicals in the digestionprocess in this document, for example to total chemical used or to thesubdivision of the sulfite component and the alkaline component are, ifnot otherwise specified, in each case calculated and stated as sodiumhydroxide (NaOH).

Acids can be metered in as acid components in order to set the desiredpH. However, preference is given to the addition of SO2, if appropriatein aqueous solution. It is inexpensive and easily available, inparticular when the used chemical solution, for example based on sodiumsulfite, is conditioned for further use following the digestion.

It is seen as an independent achievement of the invention to haverecognized the advantages of the use of a quinone component for thehigh-yield digestion according to the invention. Quinone components, inparticular anthraquinone, have until now been used in the production ofpulps with a minimal lignin content, in order to prevent undesiredaction on the carbohydrate towards the end of the digestion. By addingquinone components it becomes possible to continue the digestion of woodfurther until the approximately complete breakdown of the lignin. It hasemerged as a previously unknown, unexpected property of quinonecomponents that these raise the rate of the lignin breakdownsignificantly during the production of high-yield pulps. The duration ofthe digestion, for example during the production of coniferous woodfibrous materials, can be shortened by more than a half, depending onthe digestion conditions by more than three-quarters. This noticeableeffect is achieved with minimal use of quinone, for example. A use of,for example, anthraquinone which is between 0.005% and 0.5% is optimal.A use of anthraquinone of up to 1% also produces the desired effect. Ause of more than 3% anthraquinone is normally uneconomic.

A chemical solution is produced from an individual chemical or aplurality of the aforementioned chemicals. An aqueous solution isnormally added. As an option, the use or the addition of organicsolvents can also be provided. Alcohol, in particular methanol andethanol, in a mixture with water gives particularly effective chemicalsolutions for the production of high-quality high-yield fibrousmaterials. The mixture ratio of water and alcohol can be optimized forthe respective raw material in a few trials.

The quantity of chemicals to be used according to the invention forproducing a fibrous material with a yield of at least 70% is at least 5%for coniferous wood, at least 3.5% for deciduous wood and at least 2.5%for annual plants, in each case based on the oven-dry wood or annualplant mass to be digested. The quality of the fibrous material producedexhibits the best results with a chemical usage of up to 15% forconiferous wood, of up to 10% for deciduous wood and up to 10% forannual plants. Preferably, between 9% and 11% of chemicals, based on theoven-dry wood used, is added in the case of coniferous wood. Fordeciduous wood, the use of the chemicals is somewhat lower, preferablybetween 4% and 10%, particularly preferably between 6% and 9%, andbetween 3% and 10% in the case of annual plants.

As already explained above, the setting of a specific pH is in no wayrequired. Only when, for example, particular properties of the pulp(particularly high whiteness, a specific ratio of tearing length andtear propagation resistance) are to be achieved with the digestion mayit be expedient to add acid or an alkaline component before or duringthe digestion. According to an advantageous refinement of the invention,irrespective of the chosen use of chemicals overall, a ratio between analkaline component and sulfur dioxide (SiO2) can be set over a widerange. Here, SO2 is named as representing the acid component mentionedabove. It is therefore also possible to use an acid instead of SO2.Since the quinone component possibly added is used only in minimalquantities, normally considerably below 1%, it can be disregarded insetting this ratio. A ratio of alkaline component:SO2 in a range from5:1 to 1.6:1 is well suited to carrying out the process of the inventionand to achieving fibrous materials with high strength properties. Ausual, particularly suitable range lies between 2:1 and 1.6:1. Theproportional components are coordinated on the basis of the raw materialto be digested and the respectively chosen process management (digestiontemperature, digestion time, impregnation).

The process according to the invention can be carried out in a wide pHrange. The ratio of alkaline component to acid component and the use ofan acid or alkaline component can be set in such a way that at the startof the process a pH between 6 and 11, preferably between 7 and 11,particularly preferably between 7.5 and 10, is set. The rather alkalinepH values between 8 and 11, which are advantageous for the processaccording to the invention, also encourage the action of the quinonecomponent. The process according to the invention is tolerant withrespect to the pH; few chemicals are needed for pH adjustment. This hasa beneficial effect on the costs for chemicals.

Without any further addition of acid or alkaline component, a pH between5 and 9, normally between 6.5 and 9, for example for coniferous wood, isestablished in the free-flowing chemical solution at the end of thedigestion and also in the organic components dissolved therein, whichare liquefied by the digestion. The dissolved organic substancesprimarily include lignosulfates.

The liquor ratio, i.e. ratio of the quantity of oven-dry wood or annualplants to the chemical solution, is set between 1:1.5 and 1:6. A liquorratio of 1:2 to 1:4 is preferred. In this range, good and simple mixingand impregnation of the material to be digested is ensured. Forconiferous wood, a liquor ratio of 1:3.5 is preferred. For wood chipswith a large surface, the liquor ratio can also be considerably higher,in order to permit rapid wetting and impregnation. At the same time, theconcentration of the chemical solution can be kept so high that thequantities of liquid to be circulated do not become too large.

The mixing or impregnation of the wood or annual plant material to bedigested is preferably carried out at elevated temperatures. Heating thechips and the chemical solution to up to 110° C., preferably to up to120° C., particularly preferably to up to 130° C., leads to rapid anduniform digestion of the wood. For the mixing or impregnation of thechips, a time period of up to 30 minutes, preferably of up to 60minutes, particularly preferably of up to 90 minutes, is advantageous.The respectively optimal time period depends, amongst other things, onthe quantity of chemicals, the liquor ratio, the chosen temperature andthe type of digestion (liquid or vapor phase).

The digestion of the lignocellulosic material mixed or impregnated withthe chemical solution is preferably carried out at temperatures between120° C. and 190° C., preferably between 140° C. and 180° C. For mostwoods, digestion temperatures between 150° C. and 170° C. are set.Higher or lower temperatures can be set but in this temperature rangethe expenditure of energy for the heating and the acceleration of thedigestion are in an economic relationship with each other. Highertemperatures can additionally have a detrimental effect on the strengthsand the whiteness of the fibrous materials. The pressure generated bythe high temperatures can readily be absorbed by appropriate design ofthe digester. The duration of the heating is normally only a fewminutes, normally up to 30 minutes, advantageously up to 10 minutes, inparticular when steam heating is used. The duration of the heating canbe up to 120 minutes, preferably up to 60 minutes, for example whendigestion in the liquid phase is carried out and the chemical solutionhas to be heated together with the chips.

The duration of the digestion is primarily chosen on the basis of thedesired fibrous material properties. The duration of the digestion canbe shortened to up to 2 minutes, for example for the case of vapor-phasedigestion of deciduous wood having a low lignin content. However, it canalso be up to 180 minutes, if for example the digestion temperature islow and the natural lignin content of the wood to be digested is high.Even if the initial pH of the digestion is in the neutral range, a longdigestion time can be necessary. In particular, the digestion time is upto 90 minutes, particularly in the case of coniferous wood. Thedigestion time is particularly preferably up to 60 minutes,advantageously up to 30 minutes. A digestion time of 60 minutes issuitable in particular in the case of deciduous woods.

In the case of annual plants, the digestion time is up to 90 minutes.The use of a quinone component, in particular anthraquinone, permits areduction in the digestion time of up to 25% of the time requiredwithout the addition of anthraquinone. If the use of quinone componentsis omitted, the digestion time for comparable digestion results islengthened by more than an hour, for example from 45 minutes to 180minutes.

According to an advantageous embodiment of the process according to theinvention, the duration of the digestion is set as a function of thechosen liquor ratio. The lower the liquor ratio, the shorter the processduration can be set.

The production of high-yield fibrous material with high chemical use ofmore than 5% for coniferous wood, of more than 3.5% for deciduous woodand at least 2.5% for annual plants initially appears uneconomic.However, trials have shown that only part of the chemicals is consumedduring the partial digestion of the lignocellulosic material. Thepredominant part of the chemicals is removed unused, either before thedigestion (vapor-phase digestion) or after the digestion (digestion inthe liquid phase). The actual consumption of chemicals is below thequantities used in the digestion solution.

The chemical consumption is registered as the quantity of chemicalswhich—based on the quantity of chemicals originally used—is measuredafter the removal or separation of the chemical solution and, ifappropriate, the capture of chemical solution which is measured afterthe difibering or in conjunction with capture of the chemical solution.The chemical consumption depends on the absolute quantity of chemicalsused for the digestion, based on the oven-dry mass of wood to bedigested. The higher the use of digestion chemicals, the lower thedirect conversion of chemicals. Given a use of 27.5% of chemicals, basedon oven-dry mass of wood, for example only about 30% of the chemicalsused are consumed. Given the use of 15% of chemicals, based on oven-drymass of wood, 60% of the chemicals used are consumed, however, as couldbe verified in laboratory trials. The chemical consumption of theprocess according to the invention according to a preferred embodimentof the process during the digestion is up to 80%, preferably up to 60%,particularly preferably up to 40%, advantageously up to 20%,particularly advantageously up to 10%, of the chemical input at thestart of the digestion.

The chemical consumption for producing a tonne of fibrous material isaround 6% to 14% sulfite and/or sulfide component and also alkalineand/or acid component and also, if appropriate, quinone component, basedon oven-dry fibrous material (deciduous and coniferous wood or annualplants). According to the invention, this quantity of chemicals isenough to produce a fibrous material having the prescribed properties.In order however to ensure a uniform process result and possibly toobtain particular, desired fiber properties, it may prove to beexpedient to use higher quantities of chemicals for the digestion, forexample the aforementioned up to 30% of chemicals based on oven-dry woodor annual plant mass.

The use of these quantities of chemicals at the start of the digestionexhibits an advantageous effect, since the fibrous materials obtained inthis way have previously unavailable properties, in particular highstrength properties and high whitenesses. In particular, no digestionprocess which produces fibrous materials with high strength values overa wide pH range from neutral as far as the alkaline range has hithertobeen available. It has been shown to be economically particularlyattractive that the fibrous materials produced in accordance with theinvention can be refined to prescribed freenesses with an energy demandfar lower than known fibrous materials. In addition, they alreadydevelop the high strengths at unusually low freenesses of 12°SR to 15°SRfor coniferous wood and of 20°SR for deciduous wood.

After the mixing and impregnation of the wood with the chemical solutionor after the digestion, there is an excess of chemicals in thefree-flowing liquid. This excess is drawn off before the digestion (1stalternative) or after the digestion (2nd alternative). According to anadvantageous development of the process, the composition of the chemicalsolution removed is captured and subsequently adjusted to a prescribedcomposition for renewed use for the production of fibers. The chemicalsolution which is removed before or after the digestion of the wood orthe annual plants no longer has the composition set at the beginning. Atleast part of the chemicals used for the digestion has—as describedabove—penetrated into the material to be digested and/or has beenconsumed in the digestion. The unused chemicals can readily be usedagain for the next digestion. However, the invention proposes firstlydetermining the composition of the chemicals removed and thensupplementing the used proportions of, for example, sulfite, alkalinecomponent, quinone component or else water or alcohol, in order oncemore to produce the prescribed composition of the next digestion. Thissupplementation step is also designated strengthening.

It is to be viewed as a considerable advantage of this measure that thechemical solution, in the case of removal before the digestion but alsoin the case of removal after the digestion, really contains nosubstances at all or very few substances which prove to be disruptiveduring renewed use of the strengthened chemical solution for the nextdigestion. The process according to the invention, which is based onmaking a surplus of digestion chemicals available during theimpregnation, is also able to operate extremely economically, despitethe procedure of the high chemical use, initially appearing uneconomic,for the removal or the separation and the strengthening of the chemicalsolution can be carried out simply and cost-effectively.

The process according to the invention is controlled specifically insuch a way that only as little as possible of the starting material usedis broken down or dissolved. The aim is to produce a fibrous materialwhich, for coniferous wood, has a lignin content of at least 15%, basedon the oven-dry fiber mass, preferably a lignin content of at least 18%,particularly preferably of 21%, advantageously of at least 24%. Fordeciduous wood, the aim is to achieve a lignin content of at least 12%,based on the oven-dry fiber mass, preferably of at least 14%,particularly preferably of at least 16%, advantageously of at least 18%.In the case of annual plants, the preferred lignin content is between 10and 28%, in particular between 12 and 26%.

The yield of the process according to the invention is at least 70%,preferably more than 75%, advantageously more than 80%, in each casebased on the wood used. This yield correlates with the lignin content ofthe fibrous material specified above. The original lignin content ofwood is specific to the type. The loss of yield in the present processis predominantly represented as a loss of lignin. In the case ofnon-specific digestion processes, the proportion of hydrocarbons isincreased considerably, for example because digestion chemicals also putcellulose or hemicelluloses into solution in a manner that is undesiredper se.

A further, advantageous measure, after the defibering and possibly therefining of the lignocellulosic material, is to remove the chemicalsolution still remaining and to supply it to further use. In a preferredrefinement, this further use can include two aspects. Firstly, theorganic material broken down or put into solution during the partialdigestion, predominantly lignin, can be used further. For example, it isburned in order to obtain process energy. Or it is prepared in order tobe used in a different manner. Secondly, the used and unused chemicalsare reconditioned, so that they can be used for a renewed partialdigestion of lignocellulosic material. This includes the preparation ofconsumed chemicals.

According to a particularly preferred variant of the process accordingto the invention, the chemical solution employed is used extraordinarilyefficiently. After the defibering and possibly the refining, the fibrousmaterial is washed, in order to displace the chemical solution as far aspossible by way of water. The filtrate arising during this washing anddisplacement operation contains considerable quantities of chemicalsolution and organic material. According to the invention, this filtrateis supplied to the removed or separated chemical solution before thechemical solution is strengthened and fed to the next digestion. Thechemicals contained in the filtrate and organic constituents do notdisrupt the digestion. To the extent that they make a contribution tothe delignification during the next digestion, their content ofchemicals is registered and taken into account during the determinationof the quantity of chemicals needed for this digestion. The chemicalsfurther contained in the filtrate behave inertly during the impendingdigestion; they do not interfere. The organic constituents contained inthe filtrate likewise behave inertly. They are used further during theconditioning of the chemical solution after the next digestion, eitherto produce process energy or in another way.

It is viewed as particularly advantageous that, as a result of thismanagement of the filtrate, less fresh water and fewer chemicals areused for the digestion. At the same time, a maximum of dissolved organicmaterial is captured. This improved utilization of the organic materialsthat have gone into solution also improves the economy of the processaccording to the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned and other features and advantages of this invention,and the manner of attaining them, will become more apparent and theinvention will be better understood by reference to the followingdescription of embodiments of the invention taken in conjunction withthe accompanying drawings, wherein:

FIG. 1 shows an apparatus for carrying out the inventive method; and

FIG. 2 shows a second apparatus.

Corresponding reference characters indicate corresponding partsthroughout the several views. The exemplifications set out hereinillustrate embodiments of the invention, and such exemplifications arenot to be construed as limiting the scope of the invention in anymanner.

DETAILED DESCRIPTION OF THE INVENTION

The details of the method according to the present invention forproducing the stock suspension will be explained in more detail below inexemplary embodiments.

The following trials were evaluated in accordance with the followinginstructions:

-   -   The yield was calculated by weighing the raw material put in and        the pulp obtained after the digestion, in each case dried to        constant weight at 105° C. (absolutely dry).    -   The lignin content was determined as Klason lignin in accordance        with TAPPT T 222 om-98.

The acid-soluble lignin was determined in accordance with TAPPI UM 250.

-   -   The paper technological properties were determined on test        sheets which were produced in accordance with Zellcheming Note        Sheet V/8/76.    -   The freeness was registered as per Zellcheming Note Sheet        V/3/62.    -   The bulk was determined as per Zellcheming Instruction V/11/57.    -   The tearing length was determined as per Zellcheming Instruction        V/12/57.    -   The tear propagation resistance was determined as per DIN 53 128        Elmendorf.    -   The determination of tensile, tear and burst index was carried        out in accordance with TAPPI 220 sp-96.    -   The whiteness was determined by producing the test sheets as per        Zellcheming Note Sheet V/19/63, measured as per SCAN C 11:75        with a Datacolor elrepho 450× photometer; the whiteness is        specified in percent as per ISO Standard 2470.    -   The viscosity was determined as per Note Sheet IV/36/61 of the        German Association of Pulp and Paper Chemists and Engineers        (Zellcheming).    -   All the % statements in this document are to be read as percent        by weight if not otherwise individually indicated.    -   The statement “o.d.” in this document refers to “oven-dry”        material, which has been dried to constant weight at 105° C.    -   The chemicals for the digestion are specified in percent by        weight as sodium hydroxide if not otherwise explained.

EXAMPLE 1 Coniferous Wood Digestion in the Liquid Phase

A mixture of birch wood and Douglas fir chips, after steaming (30minutes in saturated steam at 105° C.), was dosed with a sodium sulfitedigestion solution with a liquor ratio of wood:digestion solution of1:3. The total use of chemicals was less than 15%, based on o.d. wood.The pH at the start of the digestion was adjusted to pH 8.5-9 by addingSO2.

The birch wood/chips mixture impregnated with chemical solution washeated to 170° C. over a time period of 90 minutes and digested at thismaximum temperature over 60 minutes.

The free-flowing liquid was then removed by centrifuging, collected andanalyzed and strengthened in an arrangement for feeding back unusedliquid and in this way conditioned for the next digestion.

The digested chips were defibered. Partial quantities of the fibrousmaterial produced in this way were refined for different times in orderto determine the strength at different freenesses. The expenditure ofenergy for defibering the partly digested chips was less than 300 kWh/tof fibrous material.

The yield in this trial was around 77%, based on the wood mass used.

This corresponds to a fibrous material having a lignin content of farabove 20%. The average lignin content for birch wood is given as 28%,based on the o.d. wood mass (Wagenführ, Anatomie des Holzes [Anatomy ofWood], VEB Fachbuchverlag, Leipzig, 1980). The actual lignin content ofthe fibrous material is higher than 20% since, during the digestion, itis predominantly but not exclusively lignin which is broken down.Carbohydrates (cellulose and hemicelluloses) are also dissolved in smallquantities. The values specified show that the digestion exhibits goodselectivity with regard to the breakdown of lignin and carbohydrates.

The whiteness is unexpectedly high with values over 55% ISO and thusoffers a good starting basis for possible subsequent bleaching, in whichwhitenesses of 75% ISO can be achieved.

With an initial freeness of 12°SR, these materials already have a 6 kmtearing length at a specific weight of 1.87 cm3/g.

In order to refine the fibrous materials to a freeness of 15°SR, arefining time of 20 to 30 minutes is needed. Up to a refining time of 20minutes (freeness 12°SR-15°SR), the freeness develops within a narrowrange irrespective of the pH at the start of the digestion (pH 6 to pH9.4).

Likewise irrespective of the initial pH of the digestion and therefining time needed to reach the freeness, a high strength level isreached at a freeness of 15°SR.

EXAMPLE 2

The fibrous material was produced from birch chips, the pH at the startof the digestion being 9.4.

In addition to the 15% total chemicals (sulfite and NaOH in theprescribed ratio), 0.1% anthraquinone, based on the quantity of woodused, was added.

The digestion time was 60 minutes.

The following values resulted:

Yield (%): 81.1 Lignin content: 22.7 Whiteness (% ISO): 53.7 Tearinglength (km): 9.6 Tear propagation resistance (cN; 100 g/m2): 75.0

As a result of the addition of 0.1% anthraquinone, the digestion timecan be reduced from about 180 minutes to 60 minutes under otherwiseunchanged digestion conditions. This time gain is valuable, above allbecause the fibrous material production plants can be dimensionedsmaller. Further potential savings reside in the fact that thetemperature needed for the digestion has to be maintained over only avery much shorter time period.

Furthermore, it was determined that, with a decreasing use of overallchemicals to values between 5 and 15% in the case of coniferous wood,fibrous material with largely equally good properties is produced. Theresults do not depend on the use of the anthraquinone. The anthraquinonehas the effect of accelerating the digestion but the desired fibrousmaterial can also be digested without the addition of anthraquinone.

EXAMPLE 3 Deciduous Wood Digestion in the Liquid Phase

Eucalyptus chips, after steaming, have a sodium sulfite digestionsolution added at a liquor ratio of wood:digestion solution of 1:3. Theuse of chemicals was 10.5% here (as NaOH) on o.d. chips.

Over a time period of 90 minutes, the material to be digested wasimpregnated and the digestion material was heated to the maximumdigestion temperature of 170° C. The digestion time was 50 minutes.

Digestions with eucalyptus wood show that these materials can beproduced with a specific energy input for defibering of less than 250kWh/t.

The yield in these trials was around 77%, based on the wood mass used.Given an initial freeness of 14°SR, these materials already have a 3.5km tearing length with a specific weight of 2.05 cm3/g. In thesubsequent bleaching these materials could be bleached to whitenesses of79.9% ISO.

Trials have shown that the digestions in the vapor phase exhibit a loweroverall time requirement. As compared with digestion in the liquidphase, the heating to the maximum digestion temperature is carried outvery much faster. The actual digestion then needs the same amount oftime as a digestion in the liquid phase. During the vapor phasedigestion there is no free-flowing chemical solution; this is drawn offafter the impregnation and before the digestion. It therefore has lessorganic material added than the chemical solution which is drawn offafter the digestion in the liquid phase. However, this has nosignificant influence on the quality of the fibrous material produced.

Whereas in the case of vapor phase digestions similar values in terms ofyield can be achieved, the whiteness of the fibrous materials producedin vapor-phase digestion are considerably lower, however. A significanteffect is achieved by reducing the maximum digestion temperature from170° C. to 150° C.; the whiteness rises.

The fibrous materials produced in the vapor phase exhibit excellentstrengths. The tearing length was measured as 10 km, for example, and as11 km at 15°SR. The tear propagation resistance was measured as 82.8 cNand 91.0 cN, for example. These values correspond to the best values forfibrous materials with a high lignin content which have been achievedfor digestions in the liquid phase, or are even higher. Comparablestrength values are not known from the prior art for fibrous materialswith a high lignin content.

From the examples it can be gathered particularly clearly that thefibrous materials according to the invention need only littleexpenditure of energy during refining in order to build up high tearinglengths, without the tear propagation resistance being reduced. Afreeness of 12°SR was in each case reached in 0-10 minutes; a freenessof 13°SR in 5-30 minutes, normally 10-20 minutes. In order to reach afreeness of 14°SR, the Jokro mill had to operate for 30-40 minutes andfor a freeness of 15°SR between 35 and 40 minutes were needed. It isobvious that refining to freenesses around 40°SR would require enormousexpenditure on refining energy. A particular advantage of the processaccording to the invention is therefore to be seen in the fact thatfibrous materials with high strengths can be refined with littleexpenditure of energy.

The apparatus for providing a stock suspension which is used below inthe process according to the invention for producing a tissue web,includes a pulper, in which the dry raw and semifinished materials andwaste paper are slushed in water and transformed into a state that canbe pumped. The stock formed in this way is then fed to a mixing chest.

During the subsequent refining operation, the stock suspension isrefined to a freeness of 12°SR or more.

After the machine chest, the stock suspension is diluted very highlywith white water and fed to a headbox 13.

Irrespective of how the stock suspension is obtained, it is importantfor the production of tissue paper that the stock suspension emergingfrom the headbox 13 has a freeness of less than 20°SR and a tearinglength of more than 4.5 km.

A stock suspension 1 having the abovementioned properties emerges fromthe headbox 13 in such a way that this is injected into the ingoing gapbetween a forming fabric 14 and a structured, in particular 3dimensionally structured, belt 3, by which way a tissue web 1 is formed.

The forming fabric 14 has a side oriented toward the tissue web 1 whichis smooth relative to that of the structured belt 3.

Here, the side of the structured belt 3 pointing toward the tissue web 1has deepened regions and regions elevated with respect to the deepenedregions, so that the tissue web 1 is formed in the deepened regions andthe elevated regions of the structured belt 3. The difference in heightbetween the deepened regions and the elevated regions is preferablybetween 0.07 mm and 0.6 mm. The area formed by the elevated regions ispreferably 10% or more, particularly preferably 20% or more andparticularly preferably 25% to 30%.

In the exemplary embodiments illustrated, the arrangement includingupper belt 3, tissue web 1 and forming fabric 14 is deflected around aforming roll 15 and the tissue web 1 is dewatered substantially by theforming fabric 14, before the forming fabric 14 is taken off the tissueweb 1 and the tissue web 1 is transported onward on the belt 4.

The voluminous sections of the tissue web 1 formed in the deepenedregions of the belt 3 have a higher volume and a higher grammage thanthe sections of the tissue web 1 formed in the elevated regions of thebelt 3.

Consequently, on account of its formation on the structured belt 3, thetissue web 1 already has a 3 dimensional structure.

However, the sheet formation can also take place between two smoothforming fabrics 14, so that a substantially smooth tissue web 1 withouta 3 dimensional structure is formed.

During a dewatering step following the formation of the tissue web 1,the tissue web 1 is led between the structured belt 3, which is arrangedon the top, and a lower, permeable belt 2 formed as a felt, pressurebeing exerted on the structured belt 3, the tissue web 1 and the belt 2along a dewatering section during the dewatering step, in such a waythat the tissue web 1 is dewatered in the direction of the belt 2, asindicated by the arrows in the two figures.

During the dewatering, the tissue web 1, together with the belts 2, 3,wraps around a roll 5.

Because the tissue web 1 is dewatered in the direction of the belt 2during this dewatering step and because the tissue web 1 is dewatered onthe structured belt 3 on which it has already been formed, thevoluminous sections are compressed less intensely than the othersections, so that as a result the voluminous structure of these sectionsis maintained.

The pressure for dewatering the tissue web 1 during the dewatering stepaccording to FIG. 1 is produced simultaneously, at least in somesections, by a gas flow and by a mechanical pressing force.

In this case, the gas flow flows first through the structured belt 3,then the tissue web 1 and then the lower belt 2 formed as a felt. Thegas flow through the tissue web 1 is about 150 m3 per minute and meterweb length.

In the present case, the gas flow is produced by a suction zone 10 inthe roll 5, the suction zone 10 having a length in the range between 200mm and 2500 mm, preferably between 800 mm and 1800 mm, particularlypreferably between 1200 mm and 1600 mm.

The vacuum in the suction zone 10 is between −0.2 bar and −0.8 bar,preferably between −0.4 bar and −0.6 bar.

With regard to the performance of the dewatering step carried out by wayof mechanical pressing force and optionally or additionally by way of agas flow, and also to the various configurations of apparatuses forcarrying out such a dewatering step, the entire extent ofPCT/EP2005/050198 is also to be incorporated into the disclosure contentof the present application.

According to FIG. 1, the mechanical pressing force is produced in that,during the dewatering step, the arrangement including structured belt 3,tissue web 1 and belt 2 is guided along a dewatering section 11 betweena press belt 4 under tension and a smooth surface, the press belt 4acting on the structured belt 3 and the belt 2 being supported on thesmooth surface.

Here, the smooth surface is formed by the circumferential surface of theroll 5.

The dewatering section 11 is defined substantially by the wrap region ofthe press belt 4 around the circumferential surface of the roll 5, thewrap region being defined by the spacing of the two deflection rollers12.

The press belt 4 is under a tension of at least 30 kN/m, preferably atleast 60 kN/m or 80 kN/m, and has an open area of at least 25% and acontact area of at least 10% of its total area pointing toward the upperbelt 3.

In a specific case the press belt 4, embodied as a spiral link fabric,has an open area of between 51% and 62% and a contact area of between38% and 49% of its total area pointing toward the upper belt 3.

With regard to the structure of the press belt, the entire extent ofPCT/EP2005/050198 is to be incorporated into the disclosure content ofthe present application.

The tissue web 1 leaves the dewatering section 11 with a dryness ofbetween 25% and 55%.

In a further dewatering step following the dewatering step, the tissueweb 1, together with the structured belt 3, is then led through a pressnip, the tissue web 1 in the press nip being arranged between thestructured belt 3 and a smooth roll surface of a Yankee drying cylinder7. Here, the press nip is an extended press nip formed by the Yankeedrying cylinder 7 and a shoe press roll 8.

The tissue web 1 rests on one side with a relatively great area on thecircumferential surface of the Yankee drying cylinder 7, the tissue web1 resting on the structured belt 3 on the other side.

The deepened regions and the regions elevated relative thereto of thestructured belt 3 are here formed and arranged in relation to oneanother in such a way that the voluminous sections are substantially notpressed in the press nip. On the other hand, the other sections arepressed, by which way the strength of the tissue web 1 is increasedfurther.

Between the two dewatering steps described, a further dewatering stepcan be provided, which can be carried out by way of an apparatus 9.

Optionally, provision can be made for the tissue web 1, before it runsthrough the press nip, to be led together with the structured belt 3around an evacuated deflection roll, the structured belt 3 beingarranged between the tissue web 1 and the evacuated deflection roll (notillustrated).

From FIG. 2 it can be seen that the gas flow can additionally beproduced by a positive pressure hood 6 arranged above the structuredbelt 3, the dewatering step in this case being carried out without anymechanical pressing force, i.e., as opposed to FIG. 1, no press belt 4which wraps around some section of the roll 5 being provided.

While this invention has been described with respect to at least oneembodiment, the present invention can be further modified within thespirit and scope of this disclosure. This application is thereforeintended to cover any variations, uses, or adaptations of the inventionusing its general principles. Further, this application is intended tocover such departures from the present disclosure as come within knownor customary practice in the art to which this invention pertains andwhich fall within the limits of the appended claims.

1. A process for producing a tissue web, said process comprising thesteps of: producing the web from a stock suspension including aplurality of fibers, wherein said stock suspension includeslignocellulosic fibrous material made of one of wood and annual plantswhich has one of (1) one of a tearing length of more than 6.0 km at12°SR and a tearing length of more than 7.5 km at 15°SR and a lignincontent of at least 15%, based on an oven-dry fibrous material, for aconiferous wood in an unbleached state, (2) a tearing length of morethan 4.5 km at 20°SR and a lignin content of at least 12%, based on saidoven-dry fibrous material, for a deciduous wood in said unbleachedstate, and (3) a tearing length of more than 3.5 km at 20°SR and alignin content of at least 10%, based on said oven-dry fibrous material,for said annual plants in said unbleached state.
 2. The process asclaimed in claim 1, wherein said plurality of fibers forms a fibrousmaterial, wherein said lignin content of unbleached said fibrousmaterial (1) in the case of said coniferous wood is one of at least 15%,at least 18%, and at least 21%, of said oven-dry fibrous material, (2)in the case of said deciduous wood is one of at least 12%, at least 14%,and at least 16%, of said oven-dry fibrous material, and (3) in the caseof said annual plants is one of at least 10%, at least 12%, and at least19%, of said oven-dry fibrous material.
 3. The process as claimed inclaim 1, wherein said tearing length for a coniferous wood fiber stockat 12°SR is one of greater than 7 km, greater than 7.5 km, and greaterthan 8 km.
 4. The process as claimed in claim 1, wherein said tearinglength for a coniferous wood fiber stock at 15°SR is one of greater than9 km, greater than 9.5 km, and greater than 10 km.
 5. The process asclaimed in claim 1, wherein said tearing length for a deciduous woodfiber stock at a freeness of 20°SR is one of greater than 6 km, greaterthan 7 km, and greater than 7.5 km.
 6. The process as claimed in 1,wherein said tearing length for an annual plant fiber stock at 20°SR isone of greater than 3.5 km, greater than 4 km, and greater than 4.5 km.7. A process for producing a tissue web, said process comprising thesteps of: producing the web from a stock suspension including aplurality of fibers, wherein said stock suspension includeslignocellulosic fibrous material made of one of wood or annual plantswhich has one of (1) a tearing length of more than 7.5 km at 15°SR and alignin content of at least 13%, based on an oven-dry fibrous material,for a coniferous wood in a bleached state, (2) a tearing length of morethan 5.0 km at 20°SR and a lignin content of at least 10%, based on saidoven-dry fibrous material, for a deciduous wood in said bleached state,and (3) a tearing length of more than 5.5 km at 20°SR and a lignincontent of at least 10%, based on said oven-dry fibrous material, forsaid annual plants in said bleached state.
 8. The process as claimed inclaim 7, wherein said tearing length for a coniferous wood fiber stockat 15°SR is one of greater than 9 km and greater than 10 km.
 9. Theprocess as claimed in claim 7, wherein said tearing length for adeciduous wood fiber stock at 20°SR is greater than 5.5 km.
 10. Theprocess as claimed in claim 7, wherein said tearing length for an annualplant fiber stock at 20°SR is one of greater than 4 km, greater than 4.5km, and greater than 5 km.
 11. The process as claimed in claim 7,wherein said stock suspension contains only said lignocellulosic fibrousmaterial.
 12. The process as claimed in claim 7, wherein said stocksuspension is only partly formed from said lignocellulosic fibrousmaterial.
 13. The process as claimed in claim 12, wherein said pluralityof fibers forms a fibrous material, wherein one of between 20 and 80%and between 30 and 50% of said fibrous material of said stock suspensionis formed from said lignocellulosic fibrous material.
 14. The process asclaimed in claim 7, wherein, during a dewatering step, the tissue web isled between an upper structured and permeable belt and between a lowerpermeable belt, pressure being exerted on said upper belt, the tissueweb, and said lower belt along a dewatering section.
 15. The process asclaimed in claim 14, wherein, during said dewatering step, a gas flowsfirstly through said upper belt, then the tissue web, and then saidlower belt.
 16. The process as claimed in claim 15, wherein, during saiddewatering step, an arrangement including said upper belt, the tissueweb, and said lower belt is led, at least in some sections of saidarrangement, between a press belt under tension and a smooth surface,said press belt acting on said upper belt and said lower belt beingsupported on said smooth surface.
 17. The process as claimed in claim16, wherein said gas flows through said arrangement, at least in somesections of said arrangement in said dewatering section.
 18. The processas claimed in claim 17, wherein a gas flow of said gas through thetissue web is about 150 m³ per minute and meter length along saiddewatering section.
 19. The process as claimed in claim 16, wherein saidpress belt is under a tension of one of at least 30 kN/m, at least 60kN/m, and 80 kN/m.
 20. The process as claimed in claim 16, wherein saidpress belt has an open area of more than 50% and a contact area of atleast 15%.
 21. The process as claimed in claim 16, wherein said smoothsurface is formed by a circumferential surface of a roll.
 22. Theprocess as claimed in claim 21, wherein a gas flow of said gas is formedby a suction zone in said roll.
 23. The process as claimed in claim 15,wherein a gas flow of said gas is produced by a positive pressure hoodarranged above said upper belt.
 24. A process for producing a stocksuspension including a plurality of fibers for use in producing a tissueweb, said process comprising the steps of: providing that at least aproportion of the stock suspension is produced from one of wood andannual plants having a lignin content of at least 15% for a coniferouswood, at least 12% for a deciduous wood, and at least 10% for saidannual plants, in each case based on an oven-dry fiber stock, by thefollowing steps: producing a chemical solution one of with more than 5%of chemicals (calculated as NaOH) for coniferous wood, with more than3.5% of chemicals (calculated as NaOH) for deciduous wood, and with morethan 2.5% of chemicals (calculated as NaOH) for annual plants, in eachcase based on an oven-dry quantity of said wood; mixing said chemicalsolution with one of said wood and said annual plants in a predefinedliquor ratio; heating said chemical solution and one of said wood andsaid annual plants to a temperature above room temperature; and then oneof: (1) removing a free-flowing said chemical solution and digesting oneof said wood and said annual plants in a vapor phase, and (2) digestingone of said wood and said annual plants in a liquid phase and separatingsaid free-flowing chemical solution and one of said wood and said annualplants.
 25. The process as claimed in claim 24, wherein a fibrousmaterial is produced one of (1) which has a lignin content of one of atleast 15%, at least 18%, at least 21%, and at least 24%, based on anoven-dry fibrous material, for said coniferous wood, (2) which has alignin content of one of at least 14%, at least 16%, and at least 18%,based on said oven-dry fibrous material, for said deciduous wood, and(3) which has a lignin content of one of at least 10%, at least 12%, andat least 19%, based on oven-dry fibrous material, for said annualplants.
 26. The process as claimed in claim 24, wherein a quininecomponent is used to produce said chemical solution.
 27. The process asclaimed in claim 24, wherein, in order to digest said coniferous wood,one of at most 15% of said chemicals and between 9 and 11% of saidchemicals are used.
 28. The process as claimed in claim 24, wherein, inorder to digest said deciduous wood, one of at most 10% of saidchemicals, between 4 and 10% of said chemicals, and between 6 and 9% ofsaid chemicals are used.
 29. The process as claimed in claim 24,wherein, in order to digest said annual plants, one of at most 10% ofsaid chemicals and between 3 and 10% of said chemicals are used.
 30. Theprocess as claimed in claim 24, wherein, in order to produce saidchemical solution, sulfites and sulfides are used, one of individuallyand in a mixture.
 31. The process as claimed in claim 30, wherein, inorder to produce said chemical solution, at least one of an acid, analkaline component, sulfur dioxide, sodium hydroxide, and a carbonate isused.
 32. The process as claimed in claim 24, wherein, for purposes ofdigestion, an alkaline component and an acid component are used, theacid component being SO₂, a ratio of said alkaline component:SO₂ beingset one of in a range from 5:1 to 1.6:1 and at 2:1.
 33. The process asclaimed in claim 24, wherein the process is carried out at a pH of oneof between 6 and 11, between 7 and 11, and between 7.5 and
 10. 34. Theprocess as claimed in claim 24, wherein a liquor ratio of said wood:saidchemical solution of one of between 1:1.5 and 1:6 and between 1:2 and1:4 is set.
 35. The process as claimed in claim 24, wherein saidchemical solution and one of said wood and said annual plants are heatedto up to one of 130° C., 120° C., and 110° C.
 36. The process as claimedin claim 24, wherein one of said wood and said annual plants are heatedfor up to one of 120 minutes, 60 minutes, 30 minutes, and 10 minutes.37. The process as claimed in claim 24, wherein one of said wood andsaid annual plants and said chemical solution are heated for up to oneof 120 minutes, 60 minutes, 30 minutes, and 10 minutes.
 38. The processas claimed in claim 24, wherein one of said wood and said annual plantsare digested at temperatures one of between 120° C. and 190° C., between150° C. and 180° C., and between 160° C. and 170° C.
 39. The process asclaimed in claim 24, wherein a digestion of one of said wood and saidannual plants lasts for up to one of 180 minutes, 90 minutes, 60minutes, 30 minutes, and 2 minutes.
 40. The process as claimed in claim39, wherein a digestion time is chosen as a function of said liquorratio.
 41. The process as claimed in claim 24, wherein a consumption ofsaid chemicals during a digestion is up to one of 80%, 60%, 40%, 20%,and 10% of said chemicals put in at a start of said digestion.
 42. Theprocess as claimed in claim 24, wherein a composition of said chemicalsolution that is one of removed and separated is registered andsubsequently adjusted to a prescribed composition for a renewed use forproducing a plurality of fibers.
 43. The process as claimed in claim 24,wherein said chemical solution liberated after defibering of digestedlignocellulosic material is removed and supplied to further use.
 44. Theprocess as claimed in claim 24, wherein said chemical solution liberatedafter defibering and refining of digested lignocellulosic material isremoved and supplied to further use.